"If you're smart, you won't buy +9 until lv. 40.
Just a hint..."-Ownage
I disagree with the statement. I agree with the rest though. At level 20 you really don't need a +9. However, if your looking to level fast or you plan on going into the Grave of Abyss and party/solo. Then investing in +9 as early as level 30 is worth your time. So is spending money on buff scrolls. However, what I am recommending is not for people who are just starting or only have a few bits of silver in their bank.
If you some money and are willing to pump it into your cleric to level quickly then go ahead.